Yotsugana(四つ仮名, literally "four kana") are a set of four specific kana, じ, ぢ, ず, づ (in the Nihon-shiki romanization system: zi, di, zu, du), used in the Japanese writing system. They historically represented four distinct voiced morae (syllables) in the Japanese language; however, today, in standard Japanese and the dialects of most Japanese speakers these morae have merged down to two sounds.

In the current Tokyo dialect, on which the modern standard Japanese language is based, and also in the widely spoken Kansai dialect, only two sounds are distinguished, as represented in the Hepburn (ji, ji, zu, zu) and Kunrei (zi, zi, zu, zu) romanization systems.

Modern kana usage

The spelling differences between the four kana were retained well up to the mid-twentieth century, long after the different sounds they represented had merged. That left two distinct morae in most mainland dialects, such as that of Tokyo.

Shortly after the end of World War II, the discrepancy between kana usage and pronunciation was rectified as part of a general orthographic reform, the Gendai Kanazukai, or modern kana orthography. Under the new rules, only the two kana じ zi and ず zu are to be used, but two notable exceptions exist:

When a word exhibits sequential voicing, or rendaku, as a result of compounding, a second morpheme that would otherwise begin with the kana つ tu or ち ti in isolation ( 神無月 かんなづき, kannaduki for which 月 in isolation is written つき tuki);

When the kana つ tu or ち ti is repeated and voiced in a word (続く つづく, tuduku).

An exception to was permitted for regions that pronounced the four kana as three or four distinct sounds. After a 1986 update to the Gendai Kanazukai, the exception was replaced with a statement that the unified spelling was to be primarily used but still permitting etymologically correct spellings.

Modern regional variants

The table below shows some of the different realizations and mergers of the Yotsugana characters throughout Japan.